The invention relates to a method for controlling a working machine. References to “the invention” herein should be understood to be references to one or more aspects of the invention.
The invention is applicable on working machines within the fields of industrial construction machines, in particular load receivers such as articulated haulers or dumpers. Although the invention will be described hereinafter with respect to an articulated hauler, the invention is not restricted to this particular machine, but may also be used in other heavy working machines or construction equipment.
In connection with transportation of heavy loads, a working machine in the form of an articulated hauler is frequently used. Such working machines may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines, forestry and similar environments. Thus, an articulated hauler is frequently used in rough terrain and on a slippery ground where no regular roads are present.
An articulated hauler is a frame-steered working machine having a container for receiving and transportation of a load. Such a working machine comprises a front section with a front frame and a first set of wheels, and a rear section with a rear frame and a second set of wheels. A pivot joint is arranged between the front section and the rear section allowing the front section and the rear section to pivot relative to each other about an axis extending in the vertical direction. Furthermore, the working machine comprises means for steering the working machine by pivoting the front section and the rear section relative to each other about the vertical pivot axis. The steering means normally includes a pair of hydraulic cylinders.
The front section is a tractor for driving the working machine and the rear section is provided with the container for receiving the load. In order to optimize the load capacity, the front section is normally shorter than the rear section. Usually the front section has one wheel axle, whereas the rear section has two wheel axles mounted as bogie axles. This in turn means that the pivot point is arranged asymmetrically, i.e. the distance from the wheel axle of the front section to the pivot point is shorter than the distance from the pivot point to the wheel axle/axles of the rear section. Thus, the wheels will follow different turning radii during cornering. The front wheel axle will follow a first turning radius and the bogie axles will follow a second radius, where the first radius is larger than the second radius.
In other words, during cornering the wheels of the front axle have to rotate faster than the wheels of the rear axles, and further the outer wheels have to rotate faster than the inner wheels. These geometrically required differences in rotation speed will give rise to slip between the wheels and the ground and/or constrained torque in the drive line of the working machine. In order to compensate for different rotation speeds some kind of mechanical differential can be used which allows the outer wheels to have higher rotation speed than the inner wheels.
It is desirable to provide a method and a working machine defined by way of introduction, by which method and working machine the fuel consumption can be reduced at the same time as the terrainability can be improved.
The invention, according to an aspect thereof, is based on a first insight that since the wheels of the rear section of an asymmetrical frame-steered working machine will travel in different tracks during cornering as compared to the wheels of the front wheel axle, also the wheels of the rear axles are travelling, on fresh ground not deformed and compacted by the wheels of the front wheel axle.
This in turn implies an increased rolling resistance for the wheels of the rear axles during cornering as compared to driving the working machine straight forward where the wheels of the rear axles are following the tracks of the wheels of the front wheel axle.
In accordance with an aspect of the invention, in the first control mode the rolling resistance can be reduced by controlling wheels of the rear section of the working machine to follow the tracks of the wheels of the front section. This in turn will reduce the fuel consumption due to the use of already deformed and compacted ground.
The invention, according to an aspect thereof, is further based on a second insight that if the traction for one or more wheels of the rear section and the ground is not sufficient when the front and rear wheels are following the same tracks, for many operation and ground conditions the terrainability can be improved by controlling wheels of the rear section to follow tracks which are different from the tracks of the wheels of the front section.
In accordance with an aspect of the invention, in the second mode the traction can be increased by driving wheels of the rear section on fresh ground.
Thus, an aspect of the invention enables a greater flexibility and an optimized driving of the working machine where the fuel consumption can be reduced and the terrainability can be improved when required.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.